The devices having been put into commercial use include a microanalysis chip or a device known under the name of μTAS (Micro Total Analysis Systems) wherein a fine channel or circuit is formed on a silicon and glass substrate by a microfabrication technology to perform chemical reaction, separation and analysis of such a liquid sample as a nucleic acid, protein and blood in the fine space. This kind of microchip has the advantages of reducing the amount of the sample or reagent solution to be used and the amount of waste liquid to be discharged, and providing a low-cost system characterized by space saving properties and portability. A microchip is produced by bonding two members wherein at least one of these members is provided with microfabrication.
In a conventional technique, a glass substrate has been used to produce a microchip, and various forms of microfabrication technologies have been introduced. For example, a photo resist method is used to form a fine channel on the surface of a glass substrate (Patent Literature 1). However, the glass substrate requires an extremely high product cost and is not fit for high-volume production. Thus, there is an increasingly vocal demand for development of a low-cost, disposable and resinous microchip.
Another conventional method is to form a fine channel on a PDMS (polydimethyl siloxane) substrate by optical photolithography (Patent Literature 2). However, this method has an advantage of an edge remaining on the fine channel formed by optical photolithography (so that the edge and coiner of the fine channel does not sag). However, the photolithography produces a high-cost microchip.
One of the conventional methods (Patent Literature 3) mainly intended to produce a low-cost microchip includes an injection molding technique for forming a fine channel on a plate-formed substrate. This injection molding technique is required to ensure an advanced level of transferability of the fine channel in order to keep an edge remaining on the fine channel, for example, by increasing the injection pressure and injection speed. An attempt to ensure an advanced level of transferability increases the mold releasing resistance, with the result that release of the molded product will become difficult. If undue force is applied to release the product from the mold, distortion will remain on the bonded surface (surface on one side) wherein the fine channel has been formed. Further, increase of the mold releasing resistance deforms the fine channel at the time of mold separation, and the flatness of the bonded surface of the substrate will be reduced by the wavy pattern or curvature occurring at the time of mold releasing. The bonded surface (surface on one side) is bonded with a covering material.
The resinous substrate provided with one or more cylindrical parts (chimneys) protruding in the direction perpendicular to the surface (e.g., surface on the other side) opposite the bonded surface of the substrate has a through-hole (well) which penetrates each cylindrical part along the axis of the cylindrical part from the tip end of the cylindrical part to the fine channel and communicates with the fine channel. A solution as a sample and reagent is led into the fine channel through the through-hole. This requires the cylindrical part to have the strength in excess of a prescribed level. The wall thickness of the cylindrical part must be increased to meet this requirement of strength.
If a plurality of cylindrical parts are arranged at a finer pitch, a great number of cylindrical parts can be provided on the substrate having a prescribed area. If cylindrical parts are to be arranged at a fine pitch, for example, at intervals of 0.5 mm through 10 mm, the most advantageous way is to ensure that both the inclination angle (tapering angle) of the outer wall of the cylindrical part in the direction wherein the through-hole is formed, and the inclination angle (tapering angle) of the inner wall of the through-hole in the direction wherein the through-hole is formed are set to zero; namely, that both the outer wall of the cylindrical part and the inner wall of the through-hole are formed into vertical walls. Further, when both the outer wall of the cylindrical part and the inner wall of the through-hole are formed into vertical walls, it will become easier to ensure the wall thickness of the cylindrical part.
In the injection molding of a resinous substrate, the force of bringing the inner wall of the through-hole in closer contact with the mold is increased by the shrinkage of the molded resin, and hence the resistance to the release of the through-hole from the mold is increased. This brings about a notable tendency of causing deformation of the fine channel and deterioration in the flatness of the substrate in the vicinity of the through-hole.
Particular in the injection molding of the resinous substrate provided with one or more through-holes, the inner wall of the through-hole is brought in close contact with the mold by the shrinkage of molded resin, and the resistance to the release of the through-hole from the mold is increased. This brings about a tendency of causing a considerable deformation of the fine channel of the cylindrical part and notable deterioration in the flatness of the substrate in the vicinity of the through-hole.